1. Field of the Invention
The present invention generally relates to a package substrate. More specifically, the present invention relates to a package substrate having an electromagnetic shield cover.
2. Background Information
A conventional package substrate includes a circuit board, an electronic part and an electromagnetic shield plate. The electronic part includes an IC (Integrated Circuit). The electronic part and other electronic circuits are disposed on the circuit board that has a specific shape, such as a rectangular shape. An entire board surface of the circuit board is covered by the electromagnetic shield plate. The electromagnetic shield plate is made of sheet metal. The electromagnetic shield plate is attached to the circuit board.
With this type of package substrate, the electromagnetic shield plate is given a function of blocking unnecessary radiation noise emitted from the electronic part or some other electronic circuits. This function is realized by covering the entire periphery of the electronic part or other electronic circuits with the electromagnetic shield plate in a non-contact state. On the other hand, with this package substrate, since the electronic part is located in a space surrounded by the circuit board and the electromagnetic shield plate, any heat emitted from the electronic part is trapped in the space, which diminishes a heat radiating effect. As a result, the electronic part emits so much heat that a specific temperature limit is exceeded.
One way to suppress the heat generation of the electronic part is to place the electronic part over a sheet metal heat radiating plate erected on the circuit board. With this configuration, the heat generated by the electronic part is conducted to the heat radiating plate and is radiated from the heat radiating plate. However, the heat radiating plate attached in a vertical orientation to the circuit board sticks up rather high from the board surface of the circuit board. Accordingly, placing the electronic part over the heat radiating plate that is in the vertical orientation cannot be employed when a thinner electrical or electronic device is required.
Meanwhile, with the package substrate, spacing between the circuit board and a flat roof of the electromagnetic shield plate is kept as narrow as possible, making it relatively easy to reduce thickness of the package substrate. In view of this, one idea is to utilizing the electromagnetic shield plate as a heat radiating plate for suppressing heat generation from the electronic part mounted on the circuit board, without sacrificing the reduction in the thickness of the package substrate.
Specifically, there have been conventional configurations for utilizing an electromagnetic shield plate not only to block unnecessary radiation noise, but also as a heat radiating plate (see, Japanese Laid-Open Patent Publication Nos. 2002-289753, 2003-298283 and 2002-141688). These employ a configuration in which an electromagnetic shield plate attached to a circuit board is placed directly over an electronic part mounted on the circuit board. The electronic part is sandwiched between the circuit board and the electromagnetic shield plate. With these configurations, the electromagnetic shield plate serving as a heat radiating plate does not stick up high from the circuit board, and heat generated by the electronic part is transmitted to the electromagnetic shield plate and then diffused from the electromagnetic shield plate.